1. Field of the Invention
The present invention relates to biopsy tissue verification and more specifically to devices and methods which inspect excised tissue for the presence of endogenous or exogenous contrasting agents used to better image clinically interesting regions of the body, preferably by non-destructive observation or testing of excised tissue.
2. Background of the Art
The field of detection and diagnosis of cancerous tumors, pre-malignant, malignant and other lesions and disorders is very broad and has been the subject of much research. Typically, an imaging modality including, but not limited to X-ray imaging, tomography, MRI, ultrasound, PET, nuclear imaging, palpation and visual inspection is first used to locate an area of clinical significance within the patient. Many of these techniques use the inherent biophysical contrast unique to the pathology to visualize, or diagnose the pathology. These endogenous techniques are beneficial as external contrast agents are not required and therefore directly measure pathology of interest. Once the presence of a lesion is detected with some imaging method, a biopsy is performed to extract the suspicious tissue from the patient and test it for presence of abnormal pathology. This can be done either in an open procedure or in a percutaneous, less invasive, procedure. One limitation of these methods is that optimally an excised sample should be checked whether it contains the lesion structure, before the patient can be released. This is a time consuming procedure, requires transfer of the biopsy sample from the procedure room, and does not easily fit into standard biopsy procedures. In most cases this can not be accommodated, and therefore there remains a degree of uncertainty as to whether the excised tissue does in fact include part or all of the tissue identified by the original imaging technique.
Increasingly, external exogenous contrast media are introduced into the patient in order to enhance the ability to visualize the pathology during in vivo testing/examination procedures such as MRI, X-ray, fluoroscopy and the like. Before or during a typical biopsy procedure, a contrasting agent is introduced into the bloodstream of the patient (either intravenous or intra-arterial, injection, orally or some other appropriate delivery method), with the expectation that the contrasting agent enters the lesions of interest and by the non-invasive observation of the contrast created by differential absorption into the lesion, the lesion can be more readily observed. Most imaging modalities have contrasting agents specifically designed to a) collect mainly in pathologically significant lesions and b) to create recognizable by selected modality signal different than in areas with little or no contrasting agent.
The contrast agents can stay within the tumor for different amounts of time, so that the agent either dissipates quickly or can accumulate in the areas of interest for long periods of time. The longer persistence of contrast agents can assist in long procedures such as surgical biopsy.
The contrast agents may also be used in different combinations. Combining two or more agents which are used for different imaging modalities helps in co-registration of images, better imaging and improved diagnostics. It is possible to add a component to an existing contrast agent, or modify an existing contrast agent, to make it better detectable by other methods, for example optical spectroscopy.
Contrast agents currently include and are not limited to paramagnetic molecules such as ones using chelated gadolinium. These allow for better control of relaxation times in MR imaging [“Breast Lesions: Correlation of Contrast Medium Enhancement Patterns on MR Images with Histopathological Findings and Tumor Angiogenesis.” Radiology 1996], thus providing better contrast of structures with high contrast agent concentration. For X-ray based imaging, highly x-ray absorbing compounds such as iodine, Barium, or Barium Sulfate are used. Ultrasound contrasting agents are generally formed from microbubbles, which resonate under ultrasound frequencies. Optical applications such as optical coherence tomography (OCT) use bubbles filled with light-scattering media [J. K. Barton, J. B. Hoying, and C. J. Sullivan, “Use of microbubbles as an optical coherence tomography contrast agent,” Acad. Radiol. 9, S52-5 (2002)] or fluorescing markers attaching to particular cellular features. In ultrasound, the use of microbubble contrast agents has been demonstrated in the visualization of lesions in the kidney, liver and breast. Thus far, ultrasound contrasting agents have penetrated the medical imaging field to a much lesser degree than those used for MRI.
The application of the contrast agent field is now expanding to include ultrasound as presented by Feinstein (U.S. Pat. No. 4,572,203) and Quay (U.S. Pat. No. 6,723,303) and multimodality contrast agents as presented by Meade et al. (U.S. Pat. No. 6,521,209) for optical and MRI combined contrast agent. Multi-modality contrast agents have been proposed which can be used in improved visualization in more than one modality. The clinical application of these agents has not yet been realized. These agents include:
microbubbles+gadolinium combined
gadolinium+flourophores
gadolinium+optical dye
gadolinium+antibody markers+flourophores
Contrast agents combined with antibodies have been developed to enable visualization of a specific antigen. Instead of focusing on gross pathology, actual chemical changes within cells can be targeted with these contrast agents. This aids in detection and imaging of specific biochemical processes in patient's or laboratory specimens. Efforts are currently underway to combine this concept with the multitude of contrast agents available.
In abovementioned radiological imaging techniques, there still exists a requirement of obtaining a tissue sample through biopsy to determine clinical management. This is always a difficult procedure, and it is prone to error. Problems with biopsy include at least:                inability to access all regions of tissue appropriately        inability to visualize the needle entering the lesion properly        disruption of the tissue after large needle gauge samples (vacuum-assisted)        difficulties with confirmation that the sample actually being taken from the appropriate location determined with an imaging modality        
Optical techniques have been proposed to help in the guidance of biopsy needles to targets based on endogenous signal from pathological tissues in specific applications. An overwhelming majority of research is focused on attempts to better position the needle into tissue of interest, for example by Hibner et al. (U.S. Pat. No. 0,199,754A1), demonstrates how a supplementary device such as spectroscopic fibre, can be used in conjunction with a biopsy gun to better analyze the biopsy site. However, there is little done to validate whether the actual excised tissue matches the region viewed with the imaging method guiding the biopsy. Furthermore, no attempt has been made in this patent to measure or detect the specific signature of an exogenous contrast agent.
Most imaging and sampling techniques are focused on the actual diagnosis of pathology in vivo in order to avoid or supplement the acquisition of a tissue sample. Many of these techniques perform well ex vivo, however once applied in vivo, in a much more challenging clinical environment, the techniques breakdown and lose their clinical utility. Some techniques have been also developed to examine excised tissue for pathology. These include taking a radiograph and checking for pathology induced radiographic changes such as calcifications or structural changes. Excised biopsy samples are typically examined by pathologists who inspect microscopic slides for structural changes to cells due to disease processes. The results from the examination of a sample by a pathologist determine the final diagnosis of the targeted tissue. As there may be uncertainty to whether the correct volume of tissue has been sampled, the results from the pathologist may also reflect this uncertainty.
It is in very rare circumstances that a pathologist will be able to examine the results of a biopsy sample, or surgical excision before the patient is released from the radiologist or surgeon. Therefore, the decision whether to obtain more tissue samples, or remove a larger section of tissue can not be guided by a close examination of the tissue during a typical procedure. Instead, biopsy verification is typically performed after a patient has been released. When the biopsy excision is deemed unsatisfactory, the patient is recalled to perform another procedure.
Currently, during a typical breast biopsy performed under any of the available imaging modalities, the radiologist may examine the biopsy samples visually to determine whether the samples appear to have arisen from glandular tissue, which is more likely to present abnormal pathology, or from fatty tissue which normally does not contain malignancies. This procedure may be augmented by looking at whether the samples float, or sink in the saline solution, indicating the relative density of the sample.
In a standard X-ray examination, biopsy samples obtained from lesions, which demonstrated micro-calcifications are X-rayed to validate that these micro-calcifications are present in the sample. This verifies that the samples correlate to what was evident on the mammography images. This is often done while the patient is still immobilized in the stereotactic biopsy device so the results of the tissue sample X-ray can guide the radiologist to obtain more samples from the region of interest. Performing this verification after the patient has been removed from the apparatus is not as beneficial as it cannot guide clinical management decisions at that time; however, it may impact the degree of confidence to which the radiologist may accept a pathological diagnosis that does not match the imaging presentation. The radiographic practice is extended to the surgical suite, where lesions that are surgically excised are processed in a specimen radiograph. This device is a small X-ray machine that produces an X-ray image of the excised tissue in a non-destructive manner. The image is obtained with the anticipation that there will be some X-ray imaging indication of the tumor within this sample (region of dense tissue, micro-calcification, indication of structure) from which the surgeon can verify that the correct region was removed and that proper margins were obtained around the lesion. This practice can often be helpful; however, many lesions are not well visualized using X-ray and do not present an X-ray evident presentation [M. Kriege, C. T. M. Brekelmans, C. Boetes, J. Klijn, et al. Efficacy of MRI and Mammography for Breast-Cancer Screening in Women with a Familial or Genetic Predisposition. N Engl J Med 2004; 351: 427-437].
This is becoming more problematic as modalities other than X-ray are increasingly being used to detect lesions and guide interventions (i.e., MRI, US [ultrasound], CT [computed tomography]). There is no simple way of verifying whether the biopsy sample obtained matches with the area of interest on an image used to guide the biopsy.
Techniques such as mass spectroscopy, laser induced breakdown spectroscopy, chemical assays and others are based on the destruction of the tissue. Although these methods are very accurate and sensitive to the measurement of trace amounts of chemical compounds and could be used to determine the presence of contrast agent within the sample, they are not appropriate in a clinical setting where further histopathological analysis is required for normal patient management.
Generally, compounds used as contrast agents have molecular structure alien to molecules of human tissue, or are presented in concentrations greatly differing from those normally found in the body. Therefore, the inventors suggest that the contrast agents should be detectable by methods sensitive to the molecular composition of the sample or based on large variations in concentrations of a specific chemical compound. For this purpose, application of non-destructive optical spectroscopic methods is proposed. Of course, alternative imaging technologies can be used for observation and identification of the contrast agents. Any non-destructive observation technique may be used, preferably non-destructive observation, detection and/or measurement techniques of electromagnetic radiation.
As with all other molecules, the molecules of substances used as the contrast agent should demonstrate specific spectral changes in the spectrum of the interacting radiation, when illuminated with radiation in the UV, visible and/or infrared spectra, due to the energy shift in molecular bonds when photons of electromagnetic radiation interact with a molecule. Using spectrum analysis methods those changes can be recognized, identified and used for determination of the concentration of a specific compound within a sample.
Optical techniques in medicine have been used for centuries, starting with visual inspection of skin lesions, and diagnosis based on their coloring. Currently, spectroscopic methods are used to measure the spectral dependence of absorption, transmittance, reflection, ordinary and Raman scattering of electromagnetic radiation, as well as the spectral composition of radiation produced as a result of fluorescence. The data obtained in such a way can be used for the determination of presence and concentration of specific compounds in the measured sample.
Interaction of electromagnetic radiation with tissue is already used to obtain useful information about biological systems. The typical medical applications of electromagnetic radiation in the 400-1500 nm region are optical tomography and optical biopsy for imaging; photodynamic therapy and photo-induces thermotherapy for intervention. Autofluorescence and fluorescence of injected fluorescing or phosphorescing contrast agents has also been used to provide a better contrast of suspicious lesions as compared to normal tissues both in vivo and ex vivo as shown by Alfano et al. (U.S. Pat. No. 4,930,516 and U.S. Pat. No. 6,091,985).
U.S. Pat. No. 6,214,550 (Malins) describes methods of screening for a tumor or tumor progression to the metastatic state. The screening methods are based on the characterization of DNA by principal components analysis of spectral data yielded by Fourier transform-infrared spectroscopy of DNA samples. The methods are applicable to a wide variety of DNA samples and cancer types. A model developed using multivariate normal distribution equations and discriminant analysis is particularly well suited for distinguishing primary cancerous tissue from metastatic cancerous tissue.
Photodynamic therapy requires the delivery of optically active agent into a targeted area of the body, and then using very specific light source (most often single-wavelength laser) to activate the agent and thus destroy the tissues in which the agent has collected. Many patents exist for the design of photosensitizing agents that can collect in different types of tissues and that can be activated with different types of light sources. The specificity of the agents as well as need for agents that have no adverse effects still is driving research into this method of cancer treatment.
Optical biopsy generally involves delivery of light to a tissue sample with an optical fiber or an optical relay. The light interacts with the tissue (with minimum or no destruction of tissue), and returning light is collected by an endoscope or biopsy forceps for spectroscopic analysis such as fluorescence spectroscopy as shown by Webb (U.S. Pat Appl No. 2003/10191397A1) autofluorescence shown by McMahon et al. (U.S. Pat. No. 6,174,291) or by Raman spectroscopy and others. This method is generally used in a non-invasive procedure using an endoscope or a contact probe, but has also been used for invasive procedures where the probe is placed within a biopsy needle as mentioned by Townsend et al. (U.S. Pat. No. 6,066,102). To classify tissues, either their intrinsic optical properties are used, or specifically designed optical markers, which are absorbed by the target tissue, are injected into the bloodstream and detected when they interact with light.
Previous light-based imaging applications depend either on easily detectable differences of optical properties of lesions and normal tissues or on detection of optical markers usually not recognizable by non-optical methods, but producing easily recognizable optical signal and whose concentration increases in lesions. The main concept of the present invention is to use the difference in spectral properties of tissue molecules and molecules of substances used as contrast agents for non-optical imaging methods. It is well known from physics and molecular spectroscopy that during the interaction of electromagnetic radiation with tissues, photons of different energy interact in different ways with different molecules. The photons are either absorbed, scattered or have their energy level changed by energy transfer to or from the compound molecules present. Spectroscopy allows for the quantitative analysis of such interactions and can allow the identification of compounds and structures being analyzed. There exist several spectroscopic methods, which can be used for this purpose.
Absorbance spectroscopy in the UV-visible-IR region is based on the absorption of incoming photons by the sample. Specific molecular bonds absorb incoming photons and are thus propelled into higher energetic states. When a sample is illuminated by radiation from a source producing radiation in a wide spectral range, the multiple molecules within the sample interact differently with photons of different wavelengths, causing the sample specific changes in the spectrum of the interacting radiation. By detecting these changes, it is possible to determine the presence and the concentration of a specific compound within the sample. Majority of organic and non-organic molecules produce strong basic absorption bands in mid-range and far infrared spectral ranges with much weaker overtones and combination absorption bands in near infrared and visible ranges. In case of biological samples, these signals overlap with the very strong and wide absorption bands produced by the water present in every biological tissue. The spectral overlap of signal obtained from the contrasting agent present for a specific modality and the endogenous signal of the biological sample, including its water signal, creates significant difficulties in the detection of the alien molecules of the contrasting agent; however, it is possible to overcome these problems by using high performance spectroscopy methods such as absorption spectroscopy, MR spectroscopy or other spectroscopic methods such as scattered light spectroscopy, Raman spectroscopy and other similar methods.
The difficulty in the spectroscopic determination of the presence of a compound arises when multiple compounds are present within a sample or when some compounds such as water have predominant contribution to the measured spectrum. However, the majority of substances used as contrast agents for imaging modalities have structures substantially different from those contained organic matter; therefore, they produce signals different from those produced by components of organic substances. In these cases, it is important to recognize how to extract the small spectral contribution of a contrast agent from a spectrum containing strong signal from the predominant water absorption. This can be achieved by using high performance spectroscopic methods supported by advanced data analysis techniques including but not limited to partial least square regression with numerous modifications, principal component analysis, neural networks, wavelet transforms, clustering, genetic algorithms, and similar methods alone or in combination, possibly enhanced by other techniques which enable the extraction of information distributed across a wide spectral range.
Most of the abovementioned techniques are already used in diagnosis and treatment of disease processes. Understanding of spectral characteristics of tissue allows for the determination of the structure and chemical composition of the sample. However, an area of the field of medicine that remains unexplored is the use of advanced spectrographic techniques to validate whether tissue removed from a patient in a clinical setting contains tissue of clinical interest that was seen with a given imaging modality when a contrasting agent was used. The constraints on this problem are substantially different than in vivo diagnosis, and present a clear and significant clinical benefit by enhancing the physician's ability to make more informed decisions. Furthermore, such a method may provide clear benefits in that it is a non-destructive examination of the excised sample. After a spectroscopic verification, the unchanged sample can be reintroduced back into the processing in a typical biopsy procedure.
Consequently, a method which quickly validates whether a specific biopsy sample contains an elevated concentration of an imaging contrast agent and thus comes from a region of interest as seen on a biopsy guiding image, should be very beneficial. The measured concentration of contrast agent in said biopsy sample may or should correlate with the intensity, or contrast variation observed in same region of interest in the related imaging modality in a manner that is well understood in the field of medical imaging physics. Such a method can provide better clinical guidance, provide better confidence in actual pathological diagnosis of the sample, will save unnecessary time where the patient has to wait for biopsy confirmation, and will reduce patient recalls and misdiagnosis based on examination of an improper biopsy sample. Furthermore, extension of this concept to aid in the surgical excision of pathology, with or without the use of contrast agents which are less prone to contrast-agent temporal uptake variation or introduced at the time of surgery, may lead to more accurate tumor resection.